1. Field of the Invention
The present invention relates generally to a time base error corrector and more specifically to a chrominance subcarrier phase corrector incorporated in a time base error corrector available for a video tape recorder (VTR) operated, in particular, in a chrominance subcarrier return mode such that a write pulse supplied from a phase locked loop circuit (PLL) to a time base error corrector (TBC) is feedbacked to an automatic phase controller (APC) of the VTR.
2. Description of the Prior Art
In a so-called low band conversion recording system VTR such that the chrominance subcarrier of a color TV signal is recorded in a magnetic tape after having been frequency converted to the low band side of the luminance signal, a frequency converter for inversely converting the frequency of the subcarrier to the high band side of the luminance signal in a reproduction mode is incorporated in a loop of the automatic phase controller (APC circuit), so that when the frequency of the chrominance signal is inversely converted, the phase of the chrominance signal is locked to the phase of the oscillation output of the reference oscillator by the APC circuit.
The chrominance signal thus inversely frequency converted is added to the luminance signal reproduced from the magnetic tape and then outputted as a composite video reproduction signal for the VTR.
In order to eliminate jitter included in the composite video reproduction signal outputted from the VTR as described above, conventionally time base error correctors (TBC) have been used such that the composite video reproduction signal of the VTR is written in the buffer memory in response to a write pulse signal including jitter, but the stored data are read out in response to a read pulse signal formed on the basis of the reference video signal in order to obtain the composite video signal synchronized with the reference video signal and including no jitter.
In this conventional time base error corrector, the oscillation output of a phase locked loop (PLL circuit) for receiving the horizontal synchronizing signal included in the composite video reproduction signal outputted from the VTR is used as the write pulse signal for the buffer memory, and the write pulse signal including jitter is formed on the basis of the locking operation of this PLL circuit to the horizontal synchronizing signal.
In the system configuration as described above, since the chrominance signal reproduced from the magnetic tape is phase locked by the APC circuit, no jitter is included in the chrominance signal obtained from the APC circuit. However, if the time base error correction is made by the TBC on the basis of jitter for the chrominance signal, jitter is included in the chrominance signal.
To overcome these problems, as disclosed in Japanese Published Unexamined Pat. No. 53-46224 for instance, a method of feedbacking the write pulse signal supplied from the PLL circuit to the TBC to the APC to the VTR has conventionally been adopted as a return subcarrier system. In this system, the return subcarrier signal supplied from the PLL circuit to the VTR is added to an oscillation output of a variable frequency oscillator which constructs the APC circuit of the VTR, and then supplied to the frequency converter, so that jitter can be included in the chrominance signal whose frequency is inversely converted, by controlling the output frequency of the frequency converter according to frequency fluctuations of the return subcarrier signal including jitter.
In the TBC configured as described above, however, since the principle is based upon the fact that the timing of the synchronizing signal included in the video signal after time base error has been corrected and the phase of the burst signal are both replaced by the reference video signal, the chrominance burst signal (referred to as a burst signal) included in the output video signal should match in phase the burst signal included in the reference video signal. Therefore, it may be possible to discriminate whether or not the signal is replaced correctly by comparing the phase of the burst signal included in the video signal read out of the buffer memory with the phase of the burst signal included in the reference video signal. However, even when the system is thus configured, there still exists a problem in that since the chrominance signal for the succeeding line has already been written in the buffer memory when the mismatching in phase is detected between the two, there are time intervals during which the burst signal of the output video signal does not match in phase the burst signal of the reference video signal with respect to the chrominance signals for the lines already written in the buffer memory. Thus, it is impossible to obtain correct color during the above mismatching time intervals.
On the other hand, in the TBC, in order to read the video signal from the buffer memory after the video signal outputted from the VTR has once been written in the buffer memory, the VTR is so servo-controlled that the reproduced VTR signal V.sub.MIN as shown in FIG. 8A is advanced in phase with respect to the reference video signal V.sub.REF as shown in FIG. 8B. In this method, when seeing the n-th line Ln by taking the line immediately after the vertical synchronizing signal VSYNC as a top line, the reproduced video signals V.sub.MIN are written in the buffer memory in the order of line address numbers 1, 2 . . . from the top line as shown in FIG. 9 and the data at the line address number n of the buffer memory BM is read at the timing of the n-th line Ln of the reference video signal V.sub.REF. Therefore, the time base error corrected video signal V.sub.TBC outputted from the TBC as shown in FIG. 8C can read the corresponding n-th line data from the buffer memor BM at the n-th line Ln timing of the reference video signal V.sub.REF. The above control is referred to as vertical phase control or V lock.
In the above-mentioned V lock VTR as described above, it is detected whether or not the phase of the burst signal included in the chrominance signal of the n-th line Ln of the time base error corrected video signal V.sub.TBC matches the phase of the burst signal included in the n-th line Ln of the reference video signal V.sub.REF, at the timing of reading the n-th line Ln data of the reference video signal V.sub.REF. In this case, when the former does not match the latter, even if the phase of the burst signal of the input video signal written in the buffer memory is corrected thereafter so as to match the phase of the burst signal of the reference video signal, with respect to the data written in the buffer memory BM from the time when the n-th line Ln data of the reproduced video signal V.sub.MIN has been written in the buffer memory BM to the time when the written data is read as the time base error corrected video signal V.sub.TBC, the relative phase of the chrominance signal to the burst signal of the video signal does not match the relative phase of that to the burst signal of the reference video signal V.sub.REF.